DE19900484A1 - Measuring system for residual dust monitoring for safety vacuums - Google Patents

Abstract

The invention relates to a measuring system (10) for the control of residual dust in safety vacuum cleaners. The inventive system comprises at least one grid-shaped measuring electrode (11) downstream of and behind the filter component (4). Said measuring electrode (11) is electrically insulated towards the safety vacuum cleaner and covers the entire cross-section of flow. Said measuring electrode (11) transmits a current which is produced by a contact voltage between the measuring electrode and the particles to a unit (12) analyzing said measuring value depending on the particle concentration. The measuring electrode (11) may be arranged downstream of and behind the filter (4) or behind the turbine (5) or downstream of and behind the filter (4) but in front of the turbine (5). Said turbine (5) and/or the housing (1) is directly grounded or artificially grounded in order to discharge the particles before the actual registration. The measuring current is amplified by a differential amplifier (12) and is transmitted to a unit processing the measured value, thereby prompting an optical and/or acoustic alarm and/or the disconnection of the turbine (5) and/or the automatic replacement of the filter (4) and/or the turbine (5) together with the filter (4). The progression of the measuring circuit can be saved for a statistical evaluation of the measured data and can be transmitted to an external data processing system or to a computer via an interface. The desired values and the other parameters of the appliance can be influenced by means of said external data processing system on the basis of the transmitted measured data.

Description

The invention relates to a measuring system for residual dust monitoring for Safety vacuum cleaner according to the preamble of independent claim 1.

Similar measuring devices for monitoring the dust concentration in the exhaust air in vacuum cleaners are already known and use physical Measuring principles such as measuring the differential pressure or the Radiation reflection.

When measuring the differential pressure, the prevailing pressure in front of the filter unit is included the prevailing pressure after the filter unit or after the engine compared, the differential pressure must not fall below a threshold. If the filter is not defective and not dirty, the permissible differential pressure is least, whereas the differential pressure with increasing blocking of the Filters increases. If the filter breaks, there is an impermissible pressure equalization between the chambers before and after the filter and the differential pressure drops below the permissible threshold value in the direction of zero differential pressure. The shortfall the differential pressure in the event of a broken filter, but also the exceeding of the Differential pressure with blocked filter can for alarm purposes or the Motor control can be evaluated.  

The disadvantage of the measuring principle with the differential pressure method is that the Pressure fluctuations due to engine fluctuations due to changing Volumes and speeds of the suction medium and by different Blocking and quality of the filter are so high that an exact Registration of falling below or exceeding the threshold and thus the Filter defects only insufficiently achieved, especially at small differential pressures can be.

DE-GM 92 09 407.4 is a device for detecting the filter break in Vacuum cleaners have become known which device the principle of Infrared radiation reflection used for particle measurement in the exhaust air. in the The exhaust air duct of a vacuum cleaner is an infrared transmitter and an associated one Infrared receiver on the circumference of the exhaust air duct at an angle to each other arranged, with boring energy through the infrared transmitter in the exhaust air duct is irradiated. This infrared radiation is then partially at the there dirt particles flowing through it are reflected in such a way that the reflection radiation via the infrared receiver, for example, offset by 90 ° to the infrared transmitter is registered.

The power supply and the measurement signal processing takes place in one with the Transmitter and transmitter connected evaluation electronics. By the staggered Arrangement of transmitter and receiver is due to the overlap of the the measuring field defines the respective input and output beam cone.

If the concentration of dust particles in the exhaust air duct increases, the IR energy radiated by the particles is reflected and reflected in the particles Receiver measured and thus can be a preset in the evaluation electronics Threshold value is exceeded, which triggers an alarm and / or the motor brings to a standstill. This should measure and display a filter break to harmful particle emissions into the ambient air to avoid by manually or automatically switching off the suction motor and to enable a timely filter change.

Disadvantage of the measuring principle with infrared radiation reflection for residual dust Particle measurement is that the optics of both IR transmitters and IR Can easily contaminate the receiver, thereby falsifying the measurement signal is because the dirt particles on the transmitter and receiver also IR energy  absorb and reflect, but these dirt particles are not measured should, since they are not the current flow state in the exhaust air duct reflect. This falsification of the measurement signal due to contamination can be compensated for poorly, since the degree of pollution is temporally and locally not constant cannot be defined exactly. This makes it effective metrological and / or arithmetic compensation only very poorly possible.

Another disadvantage of the measuring principle with infrared radiation reflection for residual dust Particle measurement is that the measurement is on the focus range of Sender / receiver is limited. That means that by overlapping the Radiation cone from transmitter and receiver did not define the entire measuring field Cross-section of the outlet pipe covers, so that no outside of the measuring field Particle measurement takes place, which also leads to an undefined, bad compensable falsification of the measurement signal leads.

The object of the invention is therefore a measuring system for residual dust monitoring for Safety vacuum cleaner so that the above disadvantages of the Prior art can be reduced or even avoided, namely that Measuring system is more robust and a more reliable and accurate measurement even with low particle concentration in the exhaust air.

On the one hand, the measuring system should be less susceptible to contamination and thus enable longer maintenance intervals, on the other hand also one more accurate measurement of the particle concentration in the exhaust air by over to be able to provide exact information about the condition of the filter as to whether there is a defect or not. It should also be possible to have low dust concentrations in the exhaust air determine.

The technical teaching of the independent is used to solve the task Claim 1.

An essential feature is that the measuring system according to the invention Residual dust monitoring for safety vacuums provides that at least one Measuring electrode is attached downstream behind the filter unit, which Measuring electrode one by contact voltage between the measuring electrode and particles caused current depending on the particle concentration to a measured value Processing forwards.  

This creates a contact tension through intensive contact of the Carrier medium (air) entrained dust particles with the material of the Measuring electrode. Are the dust particles made of a material that is material is different from the material of the measuring electrode, then a transition occurs of electrons that flow to the lower potential, and thus to one Current flow in the lead of the measuring electrode as a function of the touching particles and thus the particle concentration in the exhaust air. This applies to electrically conductive Particles, as well as for electrically insulating particles. With electrically conductive particles The cause of the charge separation is the different work function in the Comparison with the measuring electrode and with electrically insulating particles in the different electron affinity compared to the measuring electrode.

In a preferred embodiment of the measuring system according to the invention Residual dust monitoring for safety vacuum cleaners, it is provided that at least a measuring electrode downstream inside the outlet pipe behind the filter and is arranged behind the turbine, preferably in the end region of the outlet pipe. It should also be possible to place the measuring electrode near the turbine in the outlet pipe or to be installed in the engine block of the turbine itself.

In a further embodiment of the measuring system according to the invention Residual dust monitoring for safety vacuum cleaners, it is provided that at least a measuring electrode downstream of the filter but placed in front of the turbine is, preferably directly on or in the vicinity of the filter outlet surface. The Measuring electrode can also in an intermediate tube or an intermediate chamber be installed between the filter and the turbine or in the vicinity of the turbine in the engine block.

It is preferred that the measuring electrode cover the entire flow cross section covered, but in a way that the flow resistance in the Safety vacuum cleaner is only slightly increased and thus the efficiency of the Sucker is not affected by the measuring device.

At least one measuring electrode therefore preferably covers the entire one Filter outlet area, the cross section of the intermediate tube or the intermediate chamber between filter and turbine or the entire cross section of the exhaust pipe.  

In a preferred embodiment, the measuring electrode is designed in the form of a grid, similar to a wire mesh or perforated sheet, and lies on the inner circumference of the tube or the chamber with its lateral surface there.

The grid-shaped measuring electrode can by a ring-shaped element around the The lateral surface may be limited, the annular element preferably being made of same material as the measuring electrode, but can also, for example consist of flexible plastic into which the measuring electrode is cast and in the outlet pipe is inserted in a clamped manner. The determination of the measuring electrode can be done via a detachable or non-detachable connection, preferably however via a detachable screw, snap or clamp connection, or Welded joint.

If the measuring electrode is directly on the filter outlet surface or in its Close range, then it has approximately the same shape as the filter, so z. B. also cylindrical / tubular or disc shape and can be on its front side and / or the outer surface can be connected to the filter.

It should also be provided that several grid-like measuring electrodes are provided are, which in turn forward their measurement signal to a measurement value preparation. In addition to information about the level of the particle concentration nor the distribution of the particle concentration over the cross section of the Exhaust pipe are measured and thus the location of the filter defect is determined become. Of course, this only applies to a measuring electrode which is located between the filter and turbine located because the particles in the turbine have their flow path essential change so that a correlation between the measurement site and particle concentration behind the turbine or in the vicinity is no longer possible.

The fact that the dust particles in a certain way before contact with the Measuring electrode already in the inlet duct, in the dust chamber (housing), at Can pass through the filter and the turbine and in the exhaust duct, the dust particles are preferably discharged before contact with the measuring electrode Keep falsifications to a minimum.

This is done by grounding the parts of the safety vacuum cleaner, which are initially in Contact with the particles before they hit the measuring electrode.  

As a rule, an earthing of the turbine housing is sufficient, which at low Protection requirements are directly earthed and with high protection requirements artificial earth is laid, i.e. over protective impedances with one of the phases or the neutral conductor of the turbine motor is electrically connected.

It is also possible instead or in addition to the housing of the Safety vacuum cleaner, which usually also comes from operator Safety reasons is provided if the housing is not designed to be insulating is.

Under the above protection requirements are touch and Foreign body protection, water protection and explosion protection to understand, whereby under Explosion protection and the use of the device in a danger zone (e.g. Petrol station area), as well as the use of the device with hazardous substances (e.g. Extraction of explosive gases / liquids).

Since the electrical currents to be measured in the measuring electrode are only a few nano-amperes (nA, 10 ^-9 ) due to the contact voltage due to intensive contact of the dust particles entrained in the carrier medium (air) with the material of the measuring electrode, this must first be amplified for further processing of the measuring signal become.

A differential amplification is appropriate here, for example via a linear, inverting, differentiating operational amplifier, which inverts the measurement signal and amplifies it accordingly in relation to earth potential or artificial earth in the milli-ampere range (mA, 10 ^-3 ).

Of course, all possible designs of an operational amplifier can be be provided, such as adders, subtractors, integrators, differentiators and all combinations of it, depending on what is measured and how calculated shall be.

It goes without saying that this operational amplifier is preferably in one Microchip is housed and / or on a microprocessor, which, for. Belly performs other tasks, such as turbine control or others Measuring, control and regulation tasks. It can then, for example, continuously or only  In the event of a fault, corresponding measured values or instructions on displays on the device be issued.

This operational amplifier, microchip or microprocessor can then have a usual interface with a personal computer or another Data processing device can be connected to from there measurement, control, and To coordinate control tasks or to get measurement data from the memory of the Microchips or the microprocessor z. B. read out for statistical purposes. A calibration can also be carried out via the PC, in which the threshold values for the Further processing of the measurement signal such. B. Triggering the alarm or triggering / Switching on the turbine can be entered.

If the filter unit is defective (e.g. burst or cracked), it increases Particle concentration in the exhaust air flow increases rapidly and a lot more particles touch the measuring electrode and thus the current flow away from the measuring electrode increases, and thus the evaluation unit connected downstream in the amplifier stage. Here then the measured value (actual value) is compared with the threshold value (setpoint) and then an optical and / or acoustic alarm signal is issued. In addition to that or alternatively, the turbine engine can be turned off automatically, which by Hand must be done in the case of exclusive optical and / or acoustic alarm signals.

The present invention is preferably designed to do so to detect low filter leakage, but this measuring device can also do this used to determine the blocking of the filter, to display it, Trigger optical or acoustic alarm, turbines automatically or by hand turn off or change in the application of the suction flow or filter to change automatically or by hand. So if the filter is blocked, then a preset threshold value of the measurement signal is undershot and it can in turn optical and / or acoustic alarm signal are issued or the Turbine engine are switched off. In contrast to the turbine shutdown, at which no measurement signal is registered is with the filter blocked and the filter switched on Turbine still a low particle concentration measurable.

In embodiments of the safety vacuum cleaner with several, independent Filter units can be exceeded by exceeding the preset threshold internally automatically the suction medium to an unused / not defective  Filter unit are routed and only when the last unused filter unit alarm is also used up.

In embodiments of the safety vacuum cleaner with several, independent Turbines can be internally exceeded if the preset threshold value is exceeded automatically the suction medium to another turbine with unused / not defective filter and only when the last unused / not defective Filter unit of these turbines is also used / defective, then an alarm given.

To reduce unpleasant or harmful noises through the grid-shaped measuring electrode in the flow channel, it can be provided that in the area of the outlet duct a silencer is attached, which the Sound vibrations so affected that the noise level is below an allowable level is lowered. The arrangement of the muffler downstream is preferred on free end of the outlet duct.

The subject matter of the present invention results not only from the Subject of the individual claims, but also from the combination of individual claims among themselves.

All information disclosed in the documents, including the summary and features, in particular the spatial depicted in the drawings Education are claimed as essential to the invention, insofar as they are used individually or in Combination are new compared to the prior art.

In the following, the invention will be explained using only one embodiment illustrative drawings explained in more detail. Here go from the drawings and its description further features and advantages of the invention Invention.

Fig. 1 shows the inventive measuring system for residual dust monitoring for Safety vacuum cleaner with schematic electrical wiring. Here, the upper part of the safety vacuum cleaner is shown in section and the grid-shaped measuring electrode is attached in the free end of the outlet channel.

Fig. 2 shows a first switching principle of the earthing of the turbine for low protection requirements.

Fig. 3 shows a second switching principle of the earthing of the turbine for increased protection requirements in the form of an artificial earthing.

In Fig. 1, the inventive measuring system for residual dust monitoring for safety vacuum cleaners is only shown schematically as a block diagram to illustrate the electrical circuitry of the measuring electrode 11 and the functioning of the entire safety vacuum cleaner in conjunction with the measuring system 10 . It goes without saying that the electronic components 12 of the measuring system 10 are mounted, for example, in a separate module in or on the housing 1 of the safety vacuum cleaner, which module is HF-protected. The measuring electrode 11 itself is representative of all other embodiments here in the free end of the outlet channel 3 . The turbine 5 with a downstream, rotationally symmetrical filter element 4 sits sealed on the housing 1 of the safety vacuum cleaner, the upper part of which is shown here in section.

By operating the turbine 5 , the medium to be extracted (eg air containing dust) is sucked into the interior of the housing 1 through the inlet channel 2 in the flow direction 6 . There the heavier sucked-in dust particles fall to the ground and the lighter ones are entrained in the direction of the filter element 4 in the flow directions 7 .

Depending on the pore size of the filter 4 , larger particles are then retained in front of or within the filter 4 , smaller particles below the pore size of the filter 4 preferably penetrating through the outer surface of the filter 4 and then being sucked in the flow directions 8 in the direction of the turbine blade 5 .

In the turbine 5 , the particles are then conveyed in the direction of the outlet duct 3 , pass the area of the measuring electrode and exit the safety suction device in the direction of flow 9 . In the normal case with the filter 4 not blocked and not defective, only the smallest particles (depending on the pore size of the filter 4 ) emerge from the safety vacuum cleaner. If the filter 4 is defective, an undesirable number of particles of all sizes (depending on the defect) emerge from the safety vacuum cleaner. When the filter 4 is blocked, almost no more particles emerge from the safety vacuum cleaner.

When the particles touch the grid-shaped measuring electrode, which overlaps extends the entire cross section of the outlet channel, the effect of Charge separation as explained at the beginning and it flows in via the measuring electrode Measuring current "i" in the direction of the evaluation unit. This measuring current increases with increasing Number of times the particles touch the grid-shaped measuring electrode and thus The measuring current reflects the number of particles in the exhaust air very precisely. Due to the uniform distribution of the grid-shaped measuring electrode over the Statistical averaging is achieved over the entire cross section of the outlet duct and after a one-off calibration of the measuring system, the number of particles can be very precise can be determined, although many of the particles naturally have no measuring electrode Touch happen.

The calibration is carried out using a predefined number of medium-sized particles (depending on the pore size of the filter), which with the flowing measuring current from the Measuring electrode is correlated.

Since the measuring currents are only very small (some nA), they must first be connected via an input line 13, for. B. a differential amplifier 12 and there amplified to a few mA to give a signal to another evaluation unit via the output line 15 . The second input line 12 is connected to the turbine housing 5 and lies on earth or on artificial earth, depending on the earthing of the turbine housing 5 .

This signal can, for example, optically / acoustically indicate whether a preset threshold z. B. is exceeded in the event of a filter break, or whether it falls below by blocking the filter 4 . A control variable can also be output directly from the evaluation unit using this signal and, for. B. the turbine 5 are stopped and / or the filter 4 are automatically changed in the housing 1 .

The number of particles can also be measured continuously around these measured values in the downstream evaluation unit or one connected to it Statistically evaluate the microprocessor and / or computer.  

These measured values can then provide information, for example, about how quickly and in what way the filters 4 block and / or become defective. Such statistics can also, for. B. a production process can be traced and / or monitored in which dusty production waste is extracted. So it can e.g. B. a mathematical relationship between tool and / or tool parameters can be established with the concentration curve of the particles over time and / or location.

Fig. 2 shows a first principle of the grounding switching the turbine for low requirements, this being the casing of the turbine is grounded and the control by phase and neutral conductors and the switch S therein is shown schematically _1.2.

Fig. 3 shows a second switching principle of the earthing of the turbine 5 for increased protection requirements in the form of an artificial earthing, the housing of the turbine 5 via a protective resistor Rs and at least one further resistor R ₁ , R ₂ with the phases and the neutral conductor of the power supply the turbine 5 is connected. Depending on the ratio of the resistances R ₁ , R ₂ or the voltage divider, the potential of the artificial grounding lies between the potential of the phase and the potential of the neutral conductor.

Reference list

1

Safety vacuum cleaner housing

2nd

Inlet duct

3rd

Exhaust duct

4th

Filter element

5

turbine

6

Flow direction

7

Flow direction

8th

Flow direction

9

Flow direction

10th

Measuring system

11

Measuring electrode

12th

Differential amplifier

13

Input line

14

Input line

15

Output line
R ₁

resistance
R ₂

resistance
S ₁

switch
S ₂

switch

Claims (19)

1. Residual dust monitoring for safety vacuum cleaners, characterized in that at least one measuring electrode ( 11 ) is arranged downstream behind the filter unit ( 4 ), which measuring electrode ( 11 ) detects a current caused by contact voltage between the measuring electrode and particles, depending on the particle concentration, to a measured value processing unit ( 12 ) forwards. 2. Residual dust monitoring for safety vacuum cleaners according to claim 1, characterized in that the measuring electrode ( 11 ) is arranged downstream behind the filter ( 4 ) and behind the turbine ( 5 ). 3. Residual dust monitoring for safety vacuum cleaner according to claim 2, characterized in that the measuring electrode ( 11 ) is attached to the free end of the outlet pipe ( 3 ) in this. 4. Residual dust monitoring for safety vacuum cleaner according to claim 2, characterized in that the measuring electrode ( 11 ) in the vicinity of the turbine ( 5 ) in the outlet pipe ( 3 ) or in the engine block of the turbine ( 5 ) itself is attached. 5. Residual dust monitoring for safety vacuum cleaner according to claim 1, characterized in that the measuring electrode ( 11 ) is mounted downstream behind the filter but in front of the turbine. 6. Residual dust monitoring for safety vacuum cleaners according to claim 5, characterized in that the measuring electrode ( 11 ) is mounted directly on or in the vicinity of the output surface of the filter ( 4 ) downstream. 7. Residual dust monitoring for safety vacuum cleaners according to claim 5, characterized in that the measuring electrode ( 11 ) is mounted in an intermediate tube or an intermediate chamber between the filter ( 4 ) and the turbine ( 5 ). 8. Residual dust monitoring for safety vacuum cleaner according to claim 5, characterized in that the measuring electrode ( 11 ) is attached in the vicinity of the turbine blade in the turbine housing ( 5 ). 9. Residual dust monitoring for safety vacuum cleaners according to claims 1-8, characterized in that the measuring electrode ( 11 ) covers the entire flow cross section. 10. Residual dust monitoring for safety vacuum cleaners according to claims 1-9, characterized in that the measuring electrode ( 11 ) is grid-shaped and is mounted electrically insulated in the safety vacuum cleaner. 11. Residual dust monitoring for safety vacuum cleaners according to claims 1-10, characterized in that the turbine ( 5 ) is directly earthed or artificially earthed. 12. Residual dust monitoring for safety vacuum cleaners according to claims 1-11, characterized in that the housing ( 1 ) is directly earthed or artificially earthed. 13. Residual dust monitoring for safety vacuum cleaners according to claims 1-12, characterized in that all parts of the safety vacuum cleaner that come into contact with the particles are directly grounded or artificially grounded, with the exception of the measuring electrode ( 11 ). 14. Residual dust monitoring for safety vacuum cleaners according to claims 1-13, characterized in that the measuring current is suitably amplified in the differential amplifier ( 12 ) and forwards it to a measured value processing unit. 15. Residual dust monitoring for safety vacuum cleaner according to claim 14, characterized characterized in that the measured value processing unit clocked a target / Actual value comparison is carried out and if the setpoint is exceeded or not Output signal. 16. Residual dust monitoring for safety vacuum cleaner according to claim 15, characterized in that an optical and / or acoustic alarm is given by this output signal, and / or that the turbine ( 5 ) is switched off, and / or that the filter ( 4 ) is changed automatically. and / or the turbine ( 5 ) with filter ( 4 ) is carried out. 17. Residual dust monitoring for safety vacuum cleaners according to claims 1-16, characterized characterized in that the measuring current continuously or at time intervals directly or in the form of the correlating number of particles or in the form of the partial filter blocking or in the form of the degree of filter damage is shown on a display. 18. Residual dust monitoring for safety vacuum cleaners according to claims 1-17, characterized characterized in that the value of the measuring current is constant or in time Intervals is written into a memory, which memory is in the Safety vacuum cleaner itself or can be located externally. 19. Residual dust monitoring for safety vacuum cleaner according to claim 1-18, characterized characterized in that the evaluation unit via an interface with an external Data processing system or a computer can be coupled.